Speaker
Description
Molybdenum trioxide (MoO$_3$) is an industrially important semiconducting material, widely used in applications such as catalysis, rechargeable batteries and gas sensors. A key advantage of MoO$_3$ is the flexibility of the Mo oxidation state, which can be easily tuned. In this presentation, we will discuss the applicability of model MoO$_3$ single-crystalline thin films as supports for metal atoms and clusters, specifically, Pt and Ni. We present our latest results on the adsorption of Pt and Ni on various MoO$_3$ thin films, namely the c(2x2)-MoO$_3$ monolayer (ML), the reduced (3x3)-Mo$_5$O$_8$ ML, the MoO$_3$-bilayer (BL), and the MoO$_{3-x}$-trilayer (Magnéli phase). These films were prepared in UHV by physical vapor deposition (PVD) on a Pd(100) single crystal and further investigated by Low Energy Electron Diffraction (LEED), Scanning-Tunneling Microscopy (STM), X-Ray Photoelectron Sepctroscopy (XPS) and Infrared Reflection Absorption Spectroscopy (IRAS) using carbon monoxide (CO) as a probe molecule.
For Pt, both STM and IRAS results indicate that the (3x3)-MoO$_3$ monolayer is the most promising candidate for stabilizing Pt single atoms, while small clusters and aggregates form on all other studied MoO₃ thin film phases already at room temperature. On the (3x3)-MoO$_3$ monolayer films, the Pt atoms remain stable up to 500 K. Chemical characterization using XPS and IRAS shows that the Pt atoms remain electrically neutral rather than being oxidized, and that they bind carbon monoxide only weakly. These results will be compared with the stabilization of Ni atoms on the various MoO$_3$ films, for which a stronger interaction is expected.